1. Field of the Invention
The invention relates generally to non-semiconductor electrical and electronic components used in printed circuit board applications and particularly to an improved package and method of packaging miniature electronic components.
2. Description of Related Technology
Dual in-line chip carrier packages (DIPs) are well known in the field of electronics. A common example of a DIP is an integrated circuit, which is typically bonded to a ceramic carrier and electrically connected to a lead frame providing opposed rows of parallel electrical leads. The integrated circuit and ceramic carrier are normally encased in a black, rectangular plastic housing from which the leads extend.
The continuing miniaturization of electrical and electronic components and high density mounting thereof have created increasing challenges relating to electrical isolation and mechanical interconnection. In particular, substantial difficulty exists in establishing reliable and efficient connections between fine gauge (AWG 24 to AWG 50) copper wire leads associated with various electronic components within a given DIP. One particularly useful prior art method of packaging and connecting element leads to the lead frame terminals or, of interconnecting the leads of two or more electronic components, is disclosed in U.S. Pat. No. 5,015,981, which is illustrated herein in FIG. 1. Commonly known as xe2x80x9cinterlock basexe2x80x9d technology, this method involves routing the wire lead(s) 2 to an unused lead frame slot or channel 3 located at the edge of the non-conducting base member 10, as shown in FIGS. 1 and 2. Each of these channels 3 is designed to receive a single conductive lead frame terminal 4, which when assembled asserts an inward bias on the package thereby forcing contact between the conductive terminals 4 of the lead frame and the electronic component lead(s) 2. This method typically utilizes a locking mechanism, such as a small tab 12 or extension on the four corner lead terminals 14, 15, 16, 17, which locks into a plastic protrusion 18 of similar dimensions using the spring tension associated with the individual lead terminals 4 of the lead frame 34. The device is ultimately encapsulated within an over-molding to complete the package.
Disabilities associated with aforementioned interlock base design include the requirement to encapsulate or over-mold the package, which adds labor and cost to the product, as well as the production of unwanted mechanical and/or thermal stresses upon the electronic components and their associated conductors contained within the package due to the encapsulant. Furthermore, the electrical performance of the device may be less than that of a comparable xe2x80x9copenxe2x80x9d design as described below, due again primarily to the presence of the encapsulant.
A second approach to miniature electronic device packaging has been the so-called xe2x80x9copen headerxe2x80x9d design and is illustrated in FIG. 4. In this design, the individual lead terminals 50 of the lead frame are molded directly into a non-conductive base member 52 when the latter is formed. The leads each include a terminal pin 54 which projects from the base 52, thereby allowing the conductors 56 of the electronic component(s) 58 of the device to be routed to and wound around (or otherwise bonded to) the terminal pins 54 as required. No encapsulation or over-molding of the assembled device is performed (hence the name xe2x80x9copenxe2x80x9d, referring to the open bottom of the package.)
However, the aforementioned open header design suffers from various disabilities as well. First, excess material or xe2x80x9cflashxe2x80x9d associated with the molding of the non-conducting base member is difficult to trim due to the presence of the molded-in lead frame and terminal pins as shown in FIGS. 3 and 4. Specifically, prior art techniques of de-flashing, which typically comprise the use of sand, polymers, or another particulate abrasive sprayed at high pressure to mechanically remove the flash, undesirably damage or affect other nearby components such as the lead frame and terminal pins, thereby necessitating re-plating thereof. Obviously, such re-plating introduces additional cost into the manufacturing process.
Second, the use of the aforementioned abrasives tends to remove portions of the surface layer of the molded base member in areas adjacent to the lead frame. This is significant since in many typical constructions, glass or other fibers are used to strengthen or reinforce the polymer used to form the base element. Such removal of the surface layer allows for unwanted absorption by the exposed fiber matrix of impurities and/or moisture which can affect both the mechanical and electrical properties of the base member and the package as a whole, as well as its longevity. Such removal also detracts from the esthetics of the package, giving it an unfinished or damaged appearance.
Lastly, prior art methods of installing the lead frame on the base member and bonding the conductors of the packaged components to the lead frame make trimming of the free ends of the conductors after bonding difficult, in that they are not necessarily uniform, and do not provide a surface which readily permits such trimming.
Based on the foregoing, it would be highly desirable to provide an improved apparatus and method for connecting a lead frame to a package of any size such that the molded package could be easily de-flashed and prepared without damaging or requiring additional processing of the base member or related components such as the lead frame. Additionally, such an improved apparatus and method would facilitate trimming of the free conductor ends, thereby reducing process labor and associated cost. Ideally, no encapsulation of the device would be required, thereby further reducing manufacturing costs, and eliminating the possibility of deleterious effects on device performance and longevity associated with the use of an encapsulant.
The invention satisfies the aforementioned needs by providing an improved electronic component package and interconnect device having a plurality of specially shaped insertable leads and corresponding lead channels which receive the leads.
In a first aspect of the invention, an improved electronic device is disclosed which includes a base body with at least one side wall which is fabricated from non-conductive material and includes at least one electronic component recess and a plurality of specially shaped lead channels formed in the at least one side wall. The lead channels have at least one retention element comprising at least a projection that reduces the cross-sectional area of the lead channel. The device also includes at least one electronic component disposed in the recess, with the electronic component having a plurality of lead wires, with at least one of the lead wires extending within one of the lead channels. The lead channels are adapted to receive respective ones of insertable lead terminals, wherein each of the lead terminals comprises a clip region with substantially a U-shape, this shape enabling the clip region to frictionally connect the lead terminal to the respective lead channel and forming a conductive contact with one of the lead wires.
In a second aspect of the invention, an improved method for fabricating the aforementioned device is disclosed. In one embodiment of the method, the base member is formed from a non-conductive material using a transfer molding process. The electronic component(s) are also formed. The molded base member is de-flashed using a de-flashing tool while the lead terminals are formed and pre-shaped for simultaneous insertion into the lead channels of the base member. After de-flashing, the electronic components are placed within the base member, and the conductors routed into the lead channels thereof. Next, the lead terminals are inserted into the lead channels such that the terminals form an electrical contact with the conductors in the respective channels, and the contact is bonded using dip soldering or another bonding process. Lastly, the die bar or carrier joining the lead terminals is trimmed, and any excess conductor length is trimmed as well. The device may also optionally be encapsulated in a polymer or other over-molding if desired.
These and other objects and features of the invention will become more fully apparent from the following description and appended claims taken in conjunction with the following drawings.